ネプツニウム

解説ネプツニウム,Np．原子番号93の元素．電子配置[Rn]5f 46d7s2の周期表3族超ウラン元素の一つ．アクチノイド元素の一つ．質量数237，半減期2.14×106 y でα崩壊するもっとも長寿命の核種のほか，質量数225～244の放射性核種が知られている．1940年，E. McMillan(マクミラン)とP. Abelsonにより，カリフォルニア大学バークレー校のサイクロトロンでBeを重陽子で照射して発生させた中性子による天然ウランの衝撃で質量数239のβ崩壊核種(半減期2.4 d)が合成された．ウランの次の元素であるところから，太陽系の天王星uranusの次の惑星・海王星neptuneにちなみ，ネプツニウムと命名された．

天然物の起源At one time, neptunium’s entire existence was synthesized by man. Sometime later, in themid-twentieth century, it was discovered that a very small amount is naturally produced inuranium ore through the actions of neutrons produced by the decay of uranium in the orepitchblende. Even so, a great deal more neptunium is artificially produced every year than everdid or does exist in nature. Neptunium is recovered as a by-product of the commercial productionof plutonium in nuclear reactors. It can also be synthesized by bombarding uranium-238with neutrons, resulting in the production of neptunium-239, an isotope of neptunium witha half-life of 2.3565 days.

来歴Neptunium was first discovered in 1940 by Edwin Mattison McMillan and Philip Abelson during their research on nuclear fission. It is a decay product of uranium. When a uranium target is bombarded with slow neutrons, the target subsequently emits unusual beta rays, indicating the presence of a new isotope, thus generating its most famous isotope—neptunium-239.

使用The most important radioactive isotope of neptunium is Neptunium-237, with a half-lifeof 2.144×10+6years, or about 2.1 million years, and decays into protactinium-233 throughalpha decay. Neptunium’s most important use is in nuclear research and for instrumentsdesigned to detect neutrons.